In process measurements technology, especially for automation of chemical processes or procedures for producing a product from a raw or starting material by use of chemical, physical or biological processes and/or for control of industrial plants, measuring devices installed near to the process, so-called field devices, are applied. Field devices embodied as sensors can monitor, for example, process measurement variables, such as pressure, temperature, flow, fill level or measured variables of liquid and/or gas analysis, such as, for example, pH-value, conductivity, concentrations of certain ions and of chemical compounds and/or concentrations or partial pressures of gases.
In a process installation, a large number of the most varied of sensors are frequently applied. A sensor arranged at a certain location of the installation in the process, for example, a sensor installed at a certain location of the installation and embodied for registering one or more measured variables, forms a measuring point.
A sensor includes, as a rule, a measuring transducer, which is embodied to register the measured variable to be monitored and to produce an electrical measurement signal correlated with the current value of the measured variable. Serving for additional processing of the measurement signal is a transmitter circuit, today most often an electronic transmitter circuit, which is embodied further to condition the electrical measurement signal, for example, to digitize it, to convert it into a measured value of the measured variable and/or into a variable derived from the measured value, and, in given cases, to output such to a superordinated unit. The transmitter circuit can include, besides the measured value formation and measured value forwarding, more extensive functions. For example, it can be embodied to perform a more extensive evaluation of the measured values or to perform a sensor diagnostics, in the case of which a current state of the sensor is determined and/or a prediction made concerning the remaining life of the sensor.
In the case of sensors of the aforementioned type, especially in the field of liquid- and gas analysis, the respective transmitter circuit is frequently connected with a superordinated data processing system, which is arranged most often spatially removed from the respective measuring point and to which the measured values, diagnosis relevant data or other sensor data produced by the respective sensor are forwarded. The superordinated data processing system can especially comprise one or more electronic, process controllers, for example, one or more measurement transmitters installed on-site, a process control computer or a programmable logic controller (PLC).
Serving for data transmission frequently in such industrial measuring arrangements, at least sectionally, are fieldbus systems, such as, for example, FOUNDATION Fieldbus, PROFIBUS, ModBus, etc. or, for example, also networks based on the Ethernet standard, as well as the corresponding, most often application independently standardized, transmission protocols.
In more recent time, sensors for liquid and gas analysis have a transmitter circuit, which is accommodated in a compact housing connectable fixedly or releasably with the measuring transducer. Such a transmitter circuit accommodated in a compact housing connected fixedly or releasably with the measuring transducer and providing at least parts of the measurement transmitter functionality, especially the further processing of the measurement signal and the forwarding of the processed measurement signal to at least one superordinated unit and connectable via interfaces with the measuring transducer, on the one hand, and with the superordinated data processing unit, on the other hand, is also referred to as a compact transmitter.
Thus, known from Published International Patent Application, WO 2005/031339 A1 is a liquid sensor, which is connected via a coupling with a measurement transmitter and further with a superordinated data processing system. The sensor includes a measuring transducer, as well as, accommodated in a compact housing fixedly connected with the measuring transducer, a sensor circuit, which has a preprocessing circuit for preprocessing the analog measurement signals produced by means of the measuring transducer, an analog/digital converter for converting the registered analog measurement signals into digital measurement signals and a first interface for transferring the digital measurement signals to the superordinated measurement transmitter. The coupling includes a sensor side, primary coupling element and a complementary, secondary coupling element, which is connected with the measurement transmitter. The first interface is embodied to transmit the digital measurement signals via the coupling to the measurement transmitter. The secondary coupling element includes another electronic circuit, which includes, complementary to the first interface, a second interface, which is embodied to receive the measurement signals transmitted from the first interface. The second interface can, moreover, transmit data as well as energy via the coupling to the first interface of the sensor. The secondary coupling element can in a first embodiment be connected via a connection cable with the measurement transmitter for data communication. In a second embodiment, the secondary coupling element includes, instead of an interface connected via a cable with the measurement transmitter, a microcontroller, which is connected with a radio module having an antenna, which serves for data transmission to a superordinated unit. Not known from WO 2005/031339 A1 is an embodiment, in the case of which the compact transmitter simultaneously communicates via a cable connection and a radio connection with one or more superordinated data processing systems. Also, no information is given relative to the details of the secondary coupling element and the antenna.
Described in European Patent, EP 2 233 994 A2 is a measuring arrangement, which includes an intelligent process sensor, which is connectable releasably with a compact electronics module. The process sensor serves for determining at least one chemical or physical, measured variable of a measured medium and includes, besides a measuring transducer for registering this measured variable, an electronics unit inseparably connected with the measuring transducer. This electronics unit includes a means for monitoring the sensor state, a means for digitizing the analog measurement data from the sensor unit, a means for forwarding the analog and digitized data, at least one analog interface and at least one digital interface for connection of the process sensor with the process control system as well as galvanic isolation between the measured medium and the interfaces. The electronics unit connected inseparably with the measuring transducer serves to process measurement data, to monitor the sensor state and to store the sensor relevant data. The electronics module serves to output the data and diagnostic information provided by the intelligent sensor via one or more interfaces, for example, to a process control system or a mobile servicing device according to a communication protocol processable by the process control system, respectively the mobile servicing device. The electronics module includes a microprocessor with a memory unit, a plurality of digital interfaces, and a means for forwarding analog signals of the process sensor to a process control system. One of these digital interfaces can be designed as a radio interface with transmitting unit and antenna. EP 2 233 994 A2 gives no information concerning the exact embodiment and arrangement of the different interfaces, including the radio interface.
In operation, such sensors for liquid or gas analysis with electronics unit serving as compact transmitter are installed near to the process or even contact the process, in given cases, by applying retractable assemblies integrated in a wall of a process container. Influences of dielectrics located in the environment of the compact transmitter as a result of this installed situation can lead to a degrading of the signal quality of a radio signal output, or received, via a radio interface of the compact transmitter. At the same time, in the case of such sensors with compact transmitters, as a result of their compact construction, the space for antenna systems for a radio interface is limited, especially when an additional cable connection of the sensor with a superordinated unit should be present.